There are like... almost no pictures of mwangi, and those that do are all in tribal dress and stuff, so please try and remember that William is black.
Also as far as them being an odd pair, that's true, but remember slavery has been abolished in North America for a while now, even in the south.
William didn't so much dislike trains as he disliked sitting around inside. He'd always much preferred to be out and about doing things, or if he couldn't do that at least be outside participating. Even when they rode wagons he either liked to drive, or if that wasn't an option, sit up front, or ride on the roof; it wasn't claustrophobia, just a certain type of restlessness, his own manifestation of Michael's own drive perhaps.
When Michael ruffles his hair he knocks his hand aside in embarrassment. "Still another day Michael." he observes, spitting tobacco juice into the railway provided spitoon. "an' all we know is he's meant to be operating in Cali'. 'aint much to go on." he observes sourly, lounging in his seat.